The present invention relates to a method of enclosing semiconductor devices in a resin material, and, more particularly to a method of enclosing semiconductor devices in a resin material by molding, a lead frame for use only in practicing this method, and a semiconductor apparatus enclosed in a resin enclosure package, which can be manufactured by this method.
There has been known a semiconductor apparatus formed by hermetically enclosing semiconductor devices in a resin material (which is usually a thermosetting resin). The semiconductor apparatus of the type described above is formed by covering with the resin the semiconductor devices and a lead frame for supporting the semiconductor devices.
The method of enclosing the semiconductor devices in the resin will now be schematically described. A typical lead frame has base frames formed on the two sides thereof, a land (or a tab) on which the semiconductor devices are mounted and a multiplicity of leads. In order to obtain a plurality of products by cutting to separate the lead frame after it has been covered with a resin, the lead frame is formed as a single plate. The typical single plate is a member formed into an elongated rectangular shape having a plurality of integrally connected unit pieces each of which has a land and a multiplicity of leads formed by punching or etching. The semiconductor devices are usually placed on the lands of the lead frame and each of the semiconductor devices and a multiplicity of the corresponding leads are connected to one another by gold wires. The lead frame with the semiconductor devices is set between an upper mold half and a lower mold half (or upper and lower die halves). Although the structure of the mold has been known, it will be described later. Then, the resin is injected into each of the cavities defined by the upper and the lower mold halves through each gate, so that the upper and the lower surfaces of the lead frame including the semiconductor devices is covered with the molded resin. The molded resin is in the form of a plurality of blocks which cover each semiconductor device and each lead frame. The base frames of the lead frame, and a portion of the lead (outer lead), are not covered with the resin, and the base frames and the tie bars are removed by cutting. Furthermore, the lead frame is cut at each connecting part between the adjacent resin blocks, so that a plurality of semiconductor apparatuses can be obtained.
A technology for overcoming a problem arising when the aforesaid molding operation is performed has been disclosed in, for example, JP-B-56-43854, in which a method has been suggested which is capable of excluding voids which will be generated in the surface layer of the molded resin near the mold gate. In this method, a frame plate (that is, a projecting plate extending from the lead frame) having a bent leading portion and just like covering the outlet port of the gate is formed from the lead frame positioned adjacent to the outlet port of the gate. The bent frame plate forcibly changes the flow of the resin supplied into the cavity through the gate or causes the resin flow to collide with the inner lead, so that the flow direction is forcibly changed.
Another method of reducing the aforesaid voids has been disclosed in JP-A-60-200552, in which an additional lead is formed to project over the inner lead positioned adjacent to the gate. According to JP-A-60-200552, the resin introduced into the cavity through the gate collides with the additional lead, so that the flow of the resin is forcibly changed.
A technology relating to the shape of the lead frame has been disclosed in JP-A-60-154546. The technology disclosed in JP-A-60-154546 is capable of preventing a phenomenon of generation of a gap between the lead and the resin when the lead is undesirably extended by a tension acting on the lead which supports the land when unnecessary portions (namely the base frames and the tie bars) are removed by cutting after the resin molding process has been completed, moisture resistance of the semiconductor apparatus deteriorating due to the gap. According to JP-A-60-154546, the projection is formed on the lead which supports the land, so that the separation of the lead from the resin is prevented.
With the tendency of reducing the thickness of the semiconductor apparatus, the constraint conditions such as the weight of gold wire loops, the thickness of the semiconductor device, the thickness of the lead frame and the minimum thickness of the resin on the semiconductor device required to prevent an influence of light exerted on the semiconductor device cause arise a problem that the thickness of each resin layer covering the upper and the lower surfaces of an insert, which comprises a semiconductor device and inner leads, cannot be equalized. In other words, if the resin layers have the same thickness, the thickness of the semiconductor apparatus cannot be reduced. Therefore, the resin flow rate on the insert and under the insert become unbalanced. As a result, there arises a problem of an imperfect filling of resin in the mold cavity, generation of undesirable through-hole voids in the molded resin and of a deviation of the insert.
That is, the conventional technologies have no means which is capable of making the flows of the resin for respectively forming the upper and the lower resin layers to be substantially the same at the time of the molding operation in a case where the thickness of the resin layer above the insert and that of the resin layer under the insert are not the same.